The conversion of alcohols to aldehydes and diols has been conducted heretofore with high energy radiation in the presence of catalysts. U.S. Pat. No. 3,591,476 discloses the use of a solid catalyst such as CdO, ZnO, alpha alumina, Al.sub.2 O.sub.3, PbO, Pb.sub.3 O.sub.4, Sb.sub.2 O.sub.3, Bi.sub.2 O.sub.3, V.sub.2 O.sub.5, MoO.sub.3, CoO, CuO and CuO on copper. Suitable high energy radiation sources include accelerated electrons, gamma ray, X-rays and the like. The patent reports a significant increase in product yield when the solid catalyst is employed.
The use of photocatalysis to prepare metallized semiconductor powders, such as TiO.sub.2 powder metallized with copper, is described in U.S. Pat. No. 4,264,421. These catalysts have utility, for example, in the photocatlytic decarboxylation of saturated carboxylic acid. Metallizing of the semiconductor powder is disclosed as being achieved with illumination from a 2500 watt Hg-Xe lamp operated at 1600 watts for less than about four hours.
Such a method for the decarboxylation of saturated carboxylic acids on n-type semiconductor powders (e.g., TiO.sub.2) is described in a companion patent, U.S. Pat. No. 4,303,486. The major reaction products are the corresponding alkanes and CO.sub.2. A suspension of the catalyst in a solution containing the acid is irradiated at ambient temperature. The reaction mixture can be subjected to irradiation in the presence or absence of oxygen and the semiconductor powder, such as TiO.sub.2, can be platinized.
The photocatalytic dehydrogenation of alcohols over titanium dioxide catalysts has also been reported by independent investigators. The dehydrogenation of 2-propanol over TiO.sub.2 and metal TiO.sub.2 powders, where the metal is Ru, Rh, Pd, Ir, Pt, was reported by S. Teritani, J. Nakamishi, K. Taya and K. Tanaka, Bull. Chem. Soc. Jpn., 55, 1688 (1982). The authors found the following reactivity order: Pt/TiO.sub.2 &gt;Rh/TiO.sub.2 &gt;Pd/TiO.sub.2 /Ru/TiO.sub.2 &gt;Ir/TiO.sub.2 &gt;TiO.sub.2. The irradiation of a suspension of anatase titanium dioxide in normal primary aliphatic alcohols with ultraviolet light to produce aldehydes was reported by M. A. Malati and N. J. Seager, J. Oil Col. Chem. Assoc., 64, 231 (1981). Finally, the dehydrogenation of primary and secondary alcohols at room temperature in gaseous, liquid or aqueous phases over a catalyst comprising a dehydrogenating metal such as Pt over a photosensitive semiconductor such as TiO.sub.2 was reported by P. Pichat, J. M. Herrmann, J. Disdier, H. Courbon and M. N. Mozzenega, Nouv. J. Chim., 5, 627 (1981).
Lastly, in Netherlands Pat. No. 7,013,639 there is disclosed the oxidation of hydrocarbons, such as isobutane, in gaseous or vapor phase, said hydrocarbon being passed, admixed with oxygen and at a temperature of not more than 100.degree. C., over a metal oxide catalyst such as TiO.sub.2 irradiated with UV light, to produce acetone
Despite the teachings of the art, there has not been a recognition of the use of specific semiconductor powders for the photochemical dehydrogenation of primary and secondary alcohols in the presence of a promoter redox couple.